How big is too big??

[Snake_Griffin]

I was thinking of getting started on a new tank for my 6wk old leo, for when it gets too big for the 10gal I have now. (I want to take my time and get everything perfect thats why I'm starting now)

I was just wondering how big is too big? I wanted a tank thats about 2.5ft wide 1.5ft deep and 1ft. tall, would this big too big, I need to add that I might be thinking about getting him or her a companion depending on its sex. If its male I might get a female... though I'm not experienced enough for breeding so maybe not. If its a female I'll will for sure get another female. But if it turns out to be a male would that tank be too big for it.

Thanks in advance for everyone's help.